Snowmobiles have been known for many years. Early snowmobiles were developed with an appearance that is very primitive compared to the snowmobile of today. The snowmobile of modem times is a sophisticated vehicle with heated handle bars, twin head lights, high powered engines and many other improvements not found in the original snowmobiles.
One of the weak points in snowmobiles has been the drive system. Snowmobile drive systems have generally included a chain rpm reduction drive. The rpm of the engine must be reduced prior to applying the rotational drive to the differential sprockets driving the track. In the past the drive system has included a chain and sprocket system. The chain and sprocket system tends to wear and is subject to extreme abuse in the activities of normal snowmobile use. The rapid starts and stops, the very high rpm torque when the snowmobile leaves the ground and leaps into the air results in extremely rapid changes of speed and load.
It is also sometimes desired to include in the drive system a reverse unit for propelling the snowmobile in reverse direction under power of the engine. Reverse units of snowmobiles to date have achieved only low to moderate effectiveness.